1. Field of the Invention
This invention pertains to the maintenance of multiwire cables, such as telephone cables, and more specifically to apparatus suitable for restoring such cables to operating service following water damage.
In one aspect, this invention pertains in part to the treating of wires intended for carrying electrical current in such a manner so as to repair insulated wires that have become bare so as to restore such wires to service and so as to protect them against further electrical shorts caused by water.
2. Description of the Prior Art
Telephone cables normally comprise a large plurality of wires. Each wire is routinely individually insulated by a paper or plastic coating. Paper coatings are either paper wrapped coatings or paper cellulose extruded coatings. These individually insulated wires in pairs and sometimes in greater number are then further insulated by being wrapped in paper or otherwise to form a second layer of insulation. Finally, the double insulated wires are then enclosed in a plastic or lead jacket or sheath. An insulating gel is often pressure forced into the end of the cable to help form a moisture barrier.
In use, the wires, through switching equipment and the like, are connected in their respective pairs to one or more small dc power sources to provide the transmission current that is required and eventually to the telephone terminal equipment, namely, one or more telephone transmitters at one end or location and one or more telephone receivers at the other end.
In spite of all of the insulation protection afforded, as noted above, nevertheless, all too often, moisture does get into the cable and into the porous intrusions or even breaks in the insulation and causes a conductive path through the moisture from wire to wire. When this happens, the wires either short out altogether or crosstalk is established, thereby disrupting the telephone communications.
In order to dry the wires and correct a short or partial short, the section of cable where the problem occurred must first be isolated. The wires are then exposed, a silica gel is sprinkled into the area and a blow dryer is used to finish the drying. The silica gel electrochemically reacts with the water to heat the area and thereby accelerates the drying process by evaporation. After the moisture is removed, the exposed or bare wires are then rewrapped or spliced and the cable resealed. All of the above is time-consuming and expensive.
Moreover, in addition, it is also well-known that once a problem occurs in a cable section and remedied in the above manner, the problem will likely reoccur in the same area. It is believed that this reoccurrence results because of the abrasive nature of the silica gel and because the paper insulation become brittle, non-flexible, and flaky. Plastic coatings also become brittle and sometimes melt or partly melt either by the heat or by being dissolved. Leaving some abrasive particles in place causes the restored insulation to wear to reexpose the metal wire and permit moisture again to cause shorts.
Therefore, the standard procedures for repairing a water-damaged cable does not leave the cable in comparable pre-damaged condition. The repaired sections are weakened sections. To avoid putting weakened sections into service, whole lengths of damaged cables have to be removed. That is, drying and repairing of a previously damaged cable section is not enough. Current drying methods are so harsh that the only successful remedy is to determine where the water damage started and ended and replace the entire cable section or sections therebetween. The replacement of previously wetted sections can be extremely expensive.
Now referring to the prior art technique employed to allegedly protect cables from water migration within a cable where water has made a penetration, U.S. Pat. No. 4,308,416 to Herman, et al. describes the use of waterswellable, water-insoluble polymers in the cable or alternatively in the insulation paper to block water penetration and movement within the cable without resulting in cable breakage as a result of polymer swelling. Suitable polymers for this purpose are prepared by crosslinking an olefinically-unsaturated carboxylic acid with an alkyl acrylate and supplied in amounts of 1% to 10% of the void volume of the cable, preferably 2% to 6% of the void volume. Nevertheless, water leakage in the cable that cannot be absorbed will still cause a short to occur through any intrustion or break in the insulation.
Herman, et al. does not suggest the use of his polymers for the purpose of repairing or drying previously water-damaged cables.
It should be further noted that there is not enough polymer supplied to the affected area according to the Herman, et al. technique to cause electrochemical insulation protection to occur. Herman, et al. polymers are present to absorb some moisture and to cause some swelling to block moisture migration. However, the amount of polymer is limited by the constraints of cable size. If any more polymer were used than that taught by Herman, et al., cable breakage would result.
Therefore, it is a feature of the present invention to provide an improved apparatus and method using such apparatus for drying water-exposed electrical cable wires that does not cause electrochemical drying and that is not abrasive.
It is another feature of the present invention to provide an improved method of repairing cable wires after a short has occurred that leaves the repaired area better protected against future shorts form occurring than an unrepaired area.
It is yet another feature of the present invention to provide in one aspect thereof an improved process for protectively electrochemically coating a bare wire so that even in the presence of intrusions or breaks in the normal insulation of the wire, shorts will not occur between that wire and another wire in the cable.